A conventional type of key operated lock includes a cylinder that is mounted for rotation within an outer casing, and a group of tumbler plates are positioned in series along the length of the cylinder.
In certain locks, a side bar locking member is engaged with the sides of the tumbler plate and in the locked condition, with the key removed from the lock, the side bar is engaged with a recess in the outer casing to prevent rotation of the cylinder relative to the casing. When the key is inserted in the lock, the bits on the key move each of the tumbler plates causing notches in the side edges of the tumbler plates, to mate with the inner edge of the side bar, enabling the side bar to move inwardly, out of engagement with the recess, under the influence of a spring, to thereby unlock the cylinder from the outer casing.
To obtain the necessary number of key codes, the conventional key operated lock employs a plurality of tumbler plates, with each tumbler plate being biased inwardly by a separate spring. In some cases, the spring is engaged with the outer end of the tumbler plate, while in other locks the tumbler plate is provided with a laterally extending lug or ear and the spring is engaged with the lug.
Recently, due to design changes in vehicles, the space for the conventional door lock has been substantially reduced and the tumbler plate lock will not fit within the space limitations.